A simplified method based on ratio derivative ultraviolet spectrometry for simultaneous determination of bisphenol A (BPA) and bisphenol S (BPS) in environmental water is presented. The method provides a direct analysis of the samples without tedious sample preparation. In this method, the overlapping spectra of BPA and BPS were well resolved using the first derivative (Δλ = 1 nm) of the ratio of their absorption spectra. Measurements of absorbance were performed at wavelengths of 229.5 nm and 245.5 nm for BPA and BPS, respectively, using the ratio derivative spectrum method. Beer's law was followed in the concentration range of 8.8 X 10-7-2.2 X 10-4 mol dm-3 for BPA and 1.4 X 10-6-1.0 X 10-4 mol dm-3 for BPS. The limits of detection were 3.5 X -7 mol dm-3 for BPA and 4.4 X 10 7 mol dm 3 for BPS. Their 5:1 to 1:5 mixtures were resolved with recoveries between 90.5 % and 100.9 % for BPA and between 93.8 % and 101.1 % for BPS. The method was satisfactorily applied to the simultaneous determination of BPA and BPS in environmental water samples.